Ensoniq ESQ-M to SQ80-M Conversion Kit

Presentation

Thanks to the hard work of Rainer Buchty it’s now a known fact that there once was a plan at Ensoniq to make a rack-mount version of their famous SQ80. And as it turns out, prototypes based on the ESQ-M hardware were made, and one of these prototypes was reverse-engineered by Rainer, leading to an actual recipe to build an Ensoniq SQ80-M (or SQ-80m) from an ESQ-M.

Thanks to the very detailed explanations provided by Rainer, and after a bit of experimentation, I came out with a simple solution to convert an ESQ-M into an SQ80-M in a relatively easy, non-destructive and reversible way, which I’m introducing here.

Copyright

Disclaimer

The information and methods described herein are provided “AS-IS” WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED. Use the concepts, examples and information at your own risk. There may be errors and inaccuracies, that could be damaging to your devices. Proceed with caution, and although it is highly unlikely that accidents will happen because of following advice or procedures described in this document, the author does not take any responsibility for any damage claimed to be caused by doing so.

Design goals

My design goals was to implement a plug-in conversion kit, with an emphasis on compactness and ease of installation (ideally solder-free).

A single solder point is necessary on the ESQ-M, and it does not require the removal of the synthesizer’s mainboard from the chassis.

The kit is composed of two interface boards that insert in existing slots on the mainboard

The kit uses the SQ80-M OS as published by Rainer, and the original SQ80 waveroms (aggregated into a single EPROM).

The conversion can be reverted by simply removing the kit and replacing the original OS and wave ROMs.

Principle of operation

The kit is composed of two small “piggy-back” boards, a replacement OS EPROM and a specific waverom EPROM. The piggy-back boards extract and adapt the necessary signals to use the expanded waverom, as described in Rainer’s document.

The PiggyDOC board is inserted in the DOC slot, and accepts the DOC itself. It collects 4 signals that are then presented on the XC connector.

The PiggyWAVE board can be inserted on either of the existing waverom sockets. It receives the SQ80 waverom on its own socket and the signals coming from the PiggyDOC board on its XC connector. It also requires an additional connection, labelled SA15, to a signal coming from the ESQ-M mainboard. That signal can easily be grabbed, see below.

Installation

First, the DOC, the original OS EPROM and original waveroms must be removed from their sockets. Then, PiggyDOC is inserted in the DOC socket (U21), and the DOC is installed back into the board’s DOC socket. Next, PiggyWAVE is inserted in either one of the original wave sockets (U13/U16), and the 2Mbit EPROM containing the aggregated SQ80 waveroms is inserted into the board’s WAVEROM socket. The SA15 signal can be found on the leg of resistor R29 that’s facing toward the front of the chassis, thus it is not necessary to remove the mainboard to add this connection:

Once both the piggy-back boards are installed, the only thing left to do is to replace the original ESQ-M OS EPROM with the SQ80-M OS in U14, and connect both piggy-back boards together with a simple 4-wire cable, and voila:

Note: Of course all of the above assumes that the waveroms are socket-mounted in the original unit. If that is not the case, then some extra work is required: both roms must be desoldered first, and sockets added.